The present invention relates generally to blind fasteners and more particularly to pull-type blind fasteners in which the pulling mandrel is locked within the tubular sleeve by a locking collar being forced into a lock pocket provided on the shank of the mandrel.
Pull-type blind fasteners of the type comprising a tubular sleeve having a preformed head on one end thereof and a mandrel longitudinally movable within the sleeve so as to form a head on the other end of the sleeve in response to a pulling force applied to the mandrel are well known in the art, the same being commonly used to join a plurality of workpieces when access is restricted to only one side of the workpieces. These pull-type blind fasteners can be either mandrel retaining or non-mandrel retaining depending upon whether a portion of the mandrel is retained within the sleeve subsequent to setting of the fastener.
In mandrel retaining pull-type blind fasteners, the mandrel can be retained by friction or a mechanical lock. The present invention deals with the latter type of blind fastener. With mechanically locked mandrels, the preformed head of the sleeve is commonly provided with an enlarged diameter counterbore opening through which the mandrel projects while the mandrel is provided with a lock pocket which cooperates with the counterbore in a manner to be seen. As the fastener is set, the pulling force exerted on the mandrel causes formation of a head on the inner end of the sleeve as the mandrel and associated lock pocket are moved longitudinally into the area of the enlarged diameter counterbore. An annular locking collar positioned at least partially within the counterbore is then forced into the lock pocket so as to lock the mandrel in position relative to the sleeve. Continued pulling force on the mandrel will then cause the outwardly projecting portion thereof to separate at a controlled predetermined location proximate to the outer surface of the preformed head on the sleeve.
Commonly, a double acting tool is utilized for setting such fasteners. Examples of such fasteners being set by double acting tools are shown in the following U.S. Pat. Nos.: 3,285,121; 3,915,055. In the present invention, however, only a single acting tool is utilized in which all of the loads are taken between the mandrel and the separate locking collar. The single action tool, as utilized for installation of these fasteners, has a nose assembly provided with an opening into which the mandrel is received. This nose assembly has a forward end portion adapted to engage the annular locking collar and force it into the counterbore and the appropriately positioned lock pocket once the mandrel head forming operation is completed. Typically, the mandrel is provided with an extruding land of a slightly enlarged diameter which operates to expand the tubular sleeve as it passes therethrough. Accordingly, as this extruding land passes through the nose assembly, the opening of the nose assembly is of a size to accommodate same. However, as the collar is closely fitted to the mandrel, the extruding land operates to wipe a portion of the collar material into the opening of the tool nose assembly as it passes therethrough. With conventional collars having constant diameter openings therethrough, this collar material or collar flash is wiped into the tool nose assembly. While the tool nose assembly opening may initially be closely sized to accommodate the extruding land with a minimum clearance, normal wear initially from the extruding land and thereafter from the wiped collar material causes this clearance to progressively increase thereby resulting in reduced tool life and may even cause breakage of the nose assembly. As this clearance increases, the amount of collar material or flash increases and forms an unacceptable protrusion once the end portion of the mandrel has been separated preferably at a point substantially flush with the preformed head on the sleeve. Such collar flash must then be severed, ground or otherwise removed by a separate operation thereby increasing the installation time and associated costs.
Accordingly, the present invention provides a mechanical locking mandrel retaining pull-type blind fastener which alleviates this problem by providing an enlarged diameter opening immediately adjacent the outer end portion of the annular locking collar. In a preferred form, the locking collar is formed with symmetrical end portions each having an enlarged diameter counterbore therein which counterbores terminate at a central or intermediate portion of a diameter approximately equal to that of the mandrel. Thus, the counterbore provides an area which is radially outwardly offset with respect to both an inner or central portion of the locking collar as well as with respect to the locking collar engaging end portion of the tool nose assembly thereby precluding the wiping action of the extruding land from causing material flow between the mandrel and the end portion of the installation tool and hence eliminating the build-up of collar flash.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.